Manufacturing method for multi-material tube structures

ABSTRACT

The present invention provides an improved tubular structure which uses the properties of different materials, such as stiffness, strength, and density are exploited in a manner which combines the most attractive characteristics of existing metal and composite tubes into a metal/composite tube which contains performance characteristics (stiffness, strength or weight) not possible with pure metal or composite materials. For example, an improved tube is suitably created with a conventional metallic tube structure (e.g., steel, aluminum, titanium or the like). The original tube is modified with a secondary operation such as machining, punching, laser cutting or the like to remove various portions of the original tube wall, resulting in a tube with some pattern of “holes” or “cutaway” sections, thus resulting in a lighter tube. The tube is then suitably “fused” with composite material. For example, in one embodiment of the present invention, the metal piece is placed in a mold assembly and composite materials are molded inside the metal tube resulting in a part metal and part composite tube that has beneficial characteristics of each material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional Continuationapplication Ser. No. 11/277,220, entitled “Design and ManufacturingMethod for Multi-Material Tube Structures,” filed Mar. 22, 2006, whichis a continuation of U.S. patent application Ser. No. 10/906,753entitled “Design and Manufacturing Method for Multi-Material TubeStructures,” filed Mar. 4, 2005 and issued as U.S. Pat. No. 7,207,354 onApr. 24, 2007, which is a continuation of U.S. patent application Ser.No. 10/379,357, entitled “Design and Manufacturing Method forMulti-Material Tube Structures,” filed Mar. 4, 2003 and issued as U.S.Pat. No. 6,896,006 on May 24, 2005, which claims priority to U.S.Provisional Patent Application Ser. No. 60/361,618 entitled “Design andManufacturing Method for Multi-Material Tube Structures,” filed Mar. 4,2002, all of which are incorporated herein by reference

FIELD OF INVENTION

This invention relates generally to high performance tubular technologyexhibiting lighter and stronger properties as well as improved stiffness(longitudinally or torsionally). The characteristics of the inventionare particularly useful in tube and tube-like structures, such as golfshafts, lacrosse sticks, bicycles and bike components, ski poles, hockeysticks, softball/baseball bats, automotive and motorcycle frames andsimilar components.

BACKGROUND OF THE INVENTION

Current tubular technology used in various sporting goods, automotive,aerospace and similar applications can generally be divided into twomajor technologies: (1) metals such as steel, aluminum or titanium and(2) composites such as graphite/epoxy, fiberglass, and/or otherfiber/resin combinations.

Additionally, sub-categories of these technologies exist which can varyby processing, such as casting, forging or extruding metals, or flagwrapping, filament winding or molding composites.

The application the technology will be used in typically dictates thespecific materials and processes ultimately used. In addition to desiredperformance criteria, such as weight, strength or stiffness, otherfactors also come into the equation such as cost, cosmetic attributesand marketing appeal, as well as manufacturing issues and constraints.

Notably, differing materials have differing inherent strengths andweaknesses and product design engineers generally try to exploitparticular properties to overcome weaknesses in the materials.

For example, “Chrome-Moly” steel is an excellent material for many tuberelated products. It is strong, relatively inexpensive, available inmany sizes and variations and has a well-developed reputation withmanufacturers and designers. However, it is also a heavy material and isconsidered “old” technology for many new products/markets.

Thus, technology which better exploits the attractive properties ofmaterials, while diminishes the effects of less desirable properties,and methods for manufacturing the same, are desirable.

SUMMARY OF THE INVENTION

While the way in which the present invention addresses the disadvantagesof the prior art will be discussed in greater detail below, in general,the present invention provides tubular technology which offerssignificant advantages over prior art tubular technology.

For example, in accordance with the present invention, properties ofdifferent materials, such as stiffness, strength, and density areexploited in a manner which combines the most attractive characteristicsof existing metal and composite tubes into a metal/composite tube whichcontains performance characteristics (stiffness, strength or weight) notpossible with pure metal or composite materials.

For example, in accordance with an exemplary embodiment of the presentinvention, an improved tube is suitably created with a conventionalmetallic tube structure (e.g., steel, aluminum, titanium or the like).The original tube is modified with a secondary operation such asmachining, punching, laser cutting or the like to remove variousportions of the original tube wall, resulting in a tube with somepattern of “holes” or “cutaway” sections, thus resulting in a lightertube. The tube is then suitably “fused” with composite material. Forexample, in one embodiment of the present invention, the metal piece isplaced in a mold assembly and composite materials are molded inside themetal tube resulting in a part metal and part composite tube that hasbeneficial characteristics of each material.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present invention, however, may bestbe obtained by referring to the detailed description and claims inconnection with the drawing figures, wherein:

FIG. 1 is a conventional metal tube used in accordance with an exemplaryembodiment of the present invention;

FIG. 2 is an exemplary framing tube in accordance with an embodiment ofthe present invention;

FIG. 3 is a cross-sectional view of a framing tube and compositematerial in a mold in accordance with an exemplary embodiment of thepresent invention;

FIG. 4 is a close-up cross-sectional view of the surface and transitionpoints between framing tube and composite material in accordance with anexemplary embodiment of the present invention;

FIG. 5 is a close-up cross-sectional view of a framing tube andcomposite combination with an inner composite sleeve in accordance withan exemplary embodiment of the present invention;

FIG. 6 is a bike frame used in describing an exemplary embodiment of thepresent invention;

FIG. 7 is a graph illustrating deflection versus load curve illustratingproperties of an exemplary embodiment of the present invention withother conventional materials.

FIG. 8 is another exemplary framing tube in accordance with anembodiment of the present invention.

FIG. 9 is a close-up cross-sectional view illustrating a composite layerinsert portion in accordance with an exemplary embodiment of the presentinvention; and

FIG. 10 is a non-symmetrical golf club head in accordance with anexemplary embodiment of the present invention.

DETAILED DESCRIPTION

The following description is of exemplary embodiment of the inventiononly, and is not intended to limit the scope, applicability orconfiguration of the invention in any way. Rather, the followingdescription is intended to provide a convenient illustration forimplementing various embodiments of the invention. As will becomeapparent, various changes may be made in the function and arrangement ofthe elements described in these embodiments without departing from thescope of the invention as set forth in the appended claims.

For example, in the context of the present invention the method andapparatus hereof find particular use in connection with tubularstructures found in sporting goods (golf shafts, etc.) and frames(bicycles and the like). However, generally speaking, numerousapplications of the present invention may be realized.

For example, though “tubular” structures are generally referred toherein to mean generally cylindrical structures (e.g., golf shafts, skipoles and the like), it will be appreciated that other non-cylindricalat least partially hollow shapes (e.g., a golf club heads, hockeysticks, lacrosse sticks) which incorporate the present invention maylikewise be used. Accordingly, as used herein, “tubular” means anyshaped structure, typically comprising walls which at least partiallyenclose a volume.

Likewise, numerous manners of orienting and manufacturing tubularstructures in accordance with the present invention may be used, all ofwhich fall within the scope of the present invention.

That being said, in accordance with the present invention, in general,various materials are combined to obtain the most attractivecharacteristics of existing (or as yet unknown) metal and compositematerials into a new metal/composite tube which contains performancecharacteristics (stiffness, strength or weight) not possible with puremetal or composite materials.

In this context, the properties of different materials, includingstiffness, strength, and density are considered in accordance with thepresent invention. As used herein, they are referred to using thefollowing common letter designations and have approximate values for afew sample materials listed: Material Letter Typical Properties For:Property: Designation 4130 Steel: 0-75-T6A1 Graphite/Epoxy Stiffness E30 Msi 10 Msi 19 Msi Strength σ 190 Ksi 83 Ksi 230 Ksi Density ρ 0.289lb/ln³ 0.10 lb/ln³ 0.057 lb/ln³

As the table shows, different materials have properties that varygreatly. While, materials engineers use several other characteristics tofully define the behavior of specific materials, in the context of thepresent invention the foregoing criteria are used to illustrate thebenefits of the present invention.

Additionally, briefly, associated processes for manufacturing “tubes”from these various materials is not explained herein, however, oneskilled in the relevant art will appreciate that various conventionalmetal and/or composite forming techniques may be used in accordance withthe present invention.

With reference to FIGS. 1 and 2, illustrates the components and stepsinvolved in manufacturing an improved tube 5 in accordance with thepresent invention. For example, an improved tube in accordance with oneembodiment of the present invention comprises, a conventional tubularstructure made of steel, aluminum, titanium or the like having suitablysolid, continuous walls is provided 10. Briefly, however, as mentionedabove, conventional tubular structure 10 may alternative comprise anynumber of non-cylindrical shapes. For example, structure 10, maycomprise nearly any structure which has at least one wall which at leastpartially encloses a volume. For example, a golf club head, while not“cylindrical,” has a wall in the shape of a typical golf club head, andthe wall encloses a volume, thus resulting in a hollow structure havingthe shape of a golf club head. Likewise, structure 10 may comprise a“tubular” structure having a rectangular, square, triangular, octagonalor other cross section, as well as any combination of the same. Suchshapes are commonly found in hockey sticks, lacrosse sticks, tennisracquets and other sporting equipment as well as in framing for variousvehicles (bicycles, motorcycles, automobiles, etc.) and structures(houses, building and the like). All fall within the scope of thepresent invention and may likewise be substituted in the context of thepresent invention.

Next, tube 10 is modified with a secondary operation such as machining,punching, laser cutting or the like to remove portions of tube 10 wall,resulting in a framing tube 12 with some pattern of holes or apertures14 (also referred to herein as “cutaway” sections).

Next, composite materials 16 are molded inside tube 12 (e.g., within amold assembly) resulting in a part metal, part composite tube. Thus, inaccordance with the present invention, the orientation and amount of thematerial remaining in tube 12, the orientation and amount of compositematerial 16 used, suitably allows various properties of each material tobe enhanced in improved tube 5. For example, because composite material16 is typically lighter, stronger and stiffer than most metals improvedtube 5 is also lighter, stiffer, or stronger. In accordance with anotherbeneficial aspect of the present invention, the configuration ofimproved tube 5 is visible on the surface of tube 5 and may provide forthe placement of various indicia (e.g., product name, specifications andthe like) on the outer surface of tube 5.

Of course, as will be appreciated, the pattern of apertures 14 may varydepending on the particular properties desired. Likewise the amount ofand orientation of composite material 16 that replace the removedsections may vary as well. That said, in the present exemplaryembodiment, apertures 14 are substantially diamond shaped and arrangedin a substantially symmetrical pattern about metal tube 10. That said,apertures 14 ay take any number of shapes, sizes and configurations, andthough diamond shapes are described herein, such shapes are exemplary innature only, and not intended to limit the scope of the presentinvention.

With more particularity, and with continuing reference to FIGS. 1 and 2,a particular example of an exemplary embodiment of the present inventionis described. As mentioned above, metal tube type structure 10 isprovided and symmetrical, diamond-shaped apertures 14 are created in thewalls of tube 10 by the removal of material from tube 10, which, inturn, lowers tube's 10 weight and produces a framing tube 12 with acosmetically pleasing exterior “look.”

Next, a conventional composite material 16 (e.g., plastic, graphite orthe like), having a generally tubular shape (or otherwise similar shapeas framing tube 12) is placed within framing tube 12. Composite 16 isthen pressurized or otherwise caused to expand (e.g., through placementin an autoclave) and is thus bonded to framing tube 12, creating oneintegrated component—improved tube 5.

Of course, various steps for fabricating improved tube 5, now known oras yet unknown, may also be used. For example, with reference now toFIG. 3, framing tube 12 and composite material 16 combination may beplaced into a female mold 18 and the above steps repeated. Generally,mold 18 comprises any suitably rigid device having an inner diameterconfigured in the general shape of improved tube 5. Such molds arecommonly known and often comprises two halves 18A, B such as thoseillustrated in FIG. 3. As such, molds 18 assist in creating a desiredfinish on the outer surface of improved tube 5. Other improvements tothe fabrication may also be realized.

For example, in an exemplary embodiment, the molding process maycomprise placing layers of composite material 16 over an inflatablebladder (not shown, but commonly made of nylon, latex, silicone or thelike), placing the bladder and composite combination 16 within framingtube 12 and pressurizing the bladder to consolidate (i.e., squeeze)composite material 16 against the inner surface of framing tube 12. Asis generally known, this inflation method may use various pressurizationtechniques including a process called “trapped rubber molding” where thecomposite layers are wrapped around a rubber (usually silicone) mandrel,placed in a high temperature oven, and heated.

In any event, it should thus be appreciated that any number of “molding”operation such as those now known or as yet unknown may be used in thecontext of the present invention.

In instances such as those described above, a coefficient of thermalexpansion (CTE) for the bladder and composite material 16 (or mold 18)is much higher than framing tube 12 and a differential pressure iscreated consolidating composite material 16 and framing tube 12 into asubstantially finished product; improved tube 5.

In accordance with this embodiment of the present invention, theinternal pressure forces composite material 16 against the inner surfaceof framing tube 12, bonding the two materials together and forcing aportion of composite material through apertures 14 and pushing thelayers directly against the surface of mold 18. Improved tube 5 is thenremoved from the mold assembly and composite material 16 is visiblethrough apertures 14. Thus, in this embodiment, improved tube 5 has asubstantially consistent outside diameter.

Additionally, with reference now to FIG. 4, in accordance still furtheraspects of the present invention, improved tube 5 may be suitablymachined, ground or otherwise processed to clean up any minor transitiondiscontinuities (a portion 20 where composite material 16 meets framingtube 12) between the two materials.

In accordance with yet a further aspect of the present invention, andwith reference to FIG. 5, improved tube 5 may further comprise an innercomposite sleeve 17 which is suitably integrated with framing tube 10and composite material 16. For example, inner sleeve 17 may comprise asection of composite material similar to composite material 16 which isplaced within framing tube 10 and composite material 16. Generally,inner sleeve 17 will have a thickness similar to the thickness offraming tube 10 and/or composite material 16 and comprise the samematerial as composite material 16.

However, those skilled in the art will appreciate that inner sleeve 17may alternatively comprise other materials than composite material 16and may have different dimensions than framing tube 10 and/or compositematerial 16.

Still referring to inner sleeve 17, fabrication of improved tube 5typically remains similar to improved tubes 5 lacking inner sleeve 17.For example, inner sleeve 17 may be integrated during the“pressurization” step of bonding composite material 16 and framing tube10. Alternatively, inner sleeve 17 may be integrated in separatepressurization step after composite material 16 and framing tube 10 havebeen fabricated. Likewise, depending on the particular application anelastomeric bladder may or may not be used in the foregoing steps.

FIG. 6 illustrates an exemplary embodiment of the present invention inuse in a bicycle frame. For example, the frame that makes up the basestructure of a bicycle is made up of various tubular structures andtypically resembles that shown in FIG. 3, having a top tube 22, a seattube 24, a seat stay tube 26, a chain stay tube 28 and a down tube 30.As is generally known, an ideal bicycle frame is light, verticallycompliant (for rider comfort) and torsionally rigid (for maximum energyconversion). Preferably, each tube is individually designed to perform aparticular role (support, rigidity, impact absorption, etc.) in theframe assembly. The behavior of each of these tubes (or any tube) can befully characterized by their weight, longitudinal bend/stiffness profile(an “EI” curve) and torsional twist/stiffness profile (a “GJ” curve).

Because of the unique properties of the various engineering materialsavailable (such as those mentioned above), improved tubes 5 inaccordance with the present invention can be designed and built that addnew performance attributes to each tube. For example, in one embodiment,by removing approximately 0.5 lbs of titanium material from the downtube 30 of a bicycle frame and replacing it with a “comparable” volumeof carbon/epoxy material oriented to optimize the torsional rigidity,the weight of down tube 30 can be lowered about 0.32 lbs.

For example, titanium has a density of about 0.16 lbs/in³ and a typicalcarbon/epoxy's density is about 0.057 lbs/in³. As is well known weight(W) equals the volume (V) multiplied by the density (ρ); thus, 0.5 lb oftitanium equates to a volume of 3.125 ln³.W_(T)=V_(C)ρ_(T),orV _(T) =W _(T)/ρ_(T)=0.5 lbs/0.16 lbs.=3.125 in³

Then if we replace that same volume (3.125 in³) of titanium with carbonepoxy the new weight is:W _(C) =V _(C)ρ_(C)=(3.125 in³)(0.057 lbs/in³)=0.178 lbs.

A reduction of 0.5 lbs−0.178 lbs=0.32 lbs (or in this instance about64%), which is desirable in bicycle applications is possible.

Because carbon/epoxy material is also stiffer than the titanium(E_(C)=19 Msi v. E_(T)=16 Msi) improved tube 5 is also stiffer,particularly torsionally, due to the orientation of fibers in material16 of improved tube 5.

Similar approaches may be used for any beam defined by stiffness (longtubular or torsional) and weight criteria. In accordance with thepresent invention, improved tube 5 exploits the fact that compositematerials (such as carbon/epoxy) have higher stiffness per weight thanmetals and can therefore be designed to enhance metal designs.

In accordance with additional aspects of the present invention, improvedtube 5 also suitably retains many of the positive attributes of metaltubes, such as the ability to be welded into assemblies, or fitted withinternal/external threads for attaching fittings and couplers, whileobtaining the ability to exploit benefits of composites such as theirinfinite design flexibility. With hundreds of fibers and resins, the“composite” part of improved tube 5 can be tailored or engineered formany unique benefits. For example, as can be seen in FIG. 7, thecomposite element of the tube can be made of tough, high strainmaterials such as Kevlar™ to produce lightweight tubes with safe,non-catastrophic failure modes. Stated otherwise, improved tube 5 canwithstand higher loads with less deflection.

In summary, the ability to independently vary the longitudinal torsionaland mass distribution properties allow improved tubes 5 to achieveperformance attributes not possible with conventional metal or compositetubes such as:

-   -   Lighter golf shafts with conventional stiffness/torque values.    -   Stronger strut assemblies with metal ends and composite middles.    -   Softball bats with higher circumferential stiffness (less        deflection) to help improve energy conversion during impact.    -   Bike frames that are lighter yet stiffer.

Of course, it should be appreciated that although the examples listedhave emphasized “tubes,” the present invention is equally applicable toother “shapes” as well, which use of a dimensionally similar metalpiece, machined with various openings or cutaways which reduce weightand reveal the inner diameter, and then combine it with some moldedcomposites materials/process to yield a structure in accordance with thepresent invention. For examples, non-tube related products include:

-   -   Golf club heads such as hollow wood heads    -   Monocoque bike frame assemblies    -   Aircraft fuselages

The flexible “molding” nature of composite materials help make thisinvention possible. The adhesive systems of modern composite materialsystems allow one to “co-cure” composite materials 16 whilesimultaneously bonding them to framing tube 12.

Finally, in the foregoing specification, the invention has beendescribed with reference to specific embodiments. However, one ofordinary skill in the art appreciates that various modifications andchanges can be made without departing from the scope of the presentinvention as set forth in the claims below. Accordingly, thespecification is to be regarded in an illustrative rather than arestrictive sense, and all such modifications are intended to beincluded within the scope of the present invention.

Likewise, benefits, other advantages, and solutions to the problems havebeen described above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

1. A bicycle frame, comprising a substantially cylindrical metal tubeconnected to a substantially cylindrical composite tube, said metal tubehaving a wall with at least one aperture, wherein said composite tubeextends at least partially within said metal tube, and wherein saidcomposite tube comprises at least two layers of wrapped compositematerial.
 2. A bicycle frame according to claim 1, further comprising asecond aperture.
 3. A bicycle frame according to claim 2, wherein eachof said apertures have substantially the same shape.
 4. A bicycle frameaccording to claim 2, wherein said apertures are substantiallysymmetrical to one another.
 5. A bicycle frame according to claim 1,wherein a portion of said composite material extends through saidaperture.
 6. A bicycle frame according to claim 1, wherein a portion ofsaid composite tube extends into said aperture.
 7. A bicycle frameaccording to claim 1, wherein a portion of said composite tube is incontact with an inner surface of said metal tube.
 8. A bicycle frameaccording to claim 7, further comprising a second aperture.
 9. A bicycleframe according to claim 1, further comprising an insert havingsubstantially the same shape as said aperture, placed within saidaperture and connected to at least one of said metal tube and saidcomposite tube.
 10. A bicycle frame according to claim 9, wherein saidinsert comprises a composite material.
 11. A composite structure,comprising a non-symmetrically shaped outer metal structure that atleast partially surrounds a volume and is connected to a compositelayer, said metal structure having a wall with at least one aperture,wherein said composite layer extends at least partially within saidmetal structure.
 12. A composite structure according to claim 11,further comprising an insert having substantially the same shape as saidaperture, placed within said aperture and connected to at least one ofsaid metal structure and said composite layer.
 13. A composite structureaccording to claim 12, further comprising a second aperture.
 14. Acomposite structure according to claim 13, wherein each of saidapertures have substantially the same shape.
 15. A composite structureaccording to claim 13, wherein said apertures are substantiallysymmetrical to one another.
 16. A composite structure according to claim11, wherein a portion of said composite material extends through saidaperture.
 17. A composite structure according to claim 11, wherein aportion of said composite tube extends into said aperture.
 18. Acomposite structure according to claim 11, wherein said compositestructure comprises at least two layers of wrapped composite material.19. A composite structure according to claim 12, wherein said insertcomprises a composite material.